Sea water batteries are, in general, batteries which become operative when immersed in the sea so as to use the sea itself as the electrolyte. Various combinations of electrodes have been used but the magnesium-silver chloride couple has been found especially suitable for use to provide power for such things as torpedoes and sonobuoys. Such batteries have a number of advantages such as (1) a long shelf life, (2) no need to store an electrolyte, (3) a large power-to-weight ratio and (4) a large power-to-volume ratio.
As mentioned above, such a battery is activated by immersing it in the sea. In normal operation a certain amount of sediment or slurry is generated and, if allowed to accumulate, adversely affects operation. Such batteries also evolve bubbles of gas which, during their escape, circulate the electrolyte to some extent and also entrain and remove some of the slurry. It has been found that the operation of these batteries can be greatly improved by providing a mechanism for positively circulating the electrolyte through the battery which, among other things, has the effect of removing the slurry. Various arrangements for providing such circulation are known. In the case of torpedoes, the power may be obtained by means of a sea water scoop. Other applications, such as sonobuoys, may use a pump drawing its energy from the battery itself. Much of the prior art is concerned with the problem of maintaining the output voltage of the battery reasonably constant while the battery is connected continuously to a substantially constant load. Many arrangements for this purpose add the feature of mixing fresh electrolyte with previously circulated electrolyte in controlled proportions.
The above mentioned arrangements, while no doubt satisfactory for their respective intended purposes, are not suitable for situations in which the battery is required to supply a widely varying load. The present invention is directed to the problem of obtaining the most effective operation of a sea water battery which is called upon to operate at great depths and to supply energy to heavy and light loads alternately. For example, an active sonobuoy requires a relatively large expenditure of power during periods of transmission of sonic energy while requiring only a relatively small amount of power while receiving signals and relaying the received signals to an air or surface craft. The difficulty is compounded if the sonobuoy is required to operate at great depths. As the depth increases so does the pressure and an increase in pressure increases the solubility of the by-product gasses. It has been found that at depths of several hundred feet or more the generation of bubbles is so small as to be of little assistance in removing slurry.
It is a general object of the present invention to provide an improved system for pumping an electrolyte through a sea water battery.
A more specific object is to provide a system particularly suitable for use with a battery which is required to supply widely varying loads.